232 ARTHUR WILLET. 



The stnicture in the larva of Aniphioxus known as 

 Hatschek's nephridium/ which opens at one end into the 

 buccal cavity, has been shown by MacBride ^ to be, at an 

 early stage, in open primary communication at its other end 

 with the left archenteric pouch, which he has suggestively 

 named the left collar-cavity. In spite of differences in the 

 method of development, I regard Hatschek's nephridium as 

 being in principle the vestige of a pair of collar canals. 



Bateson tentatively compared the collar-pores of the 

 Enteropneusta both to Hatschek^s nephridium and to Lan- 

 kester's brown funnels. The comparison of the enteropneustic 

 proboscis-pore with the orifice of the amphioxine prseoral pit 

 is of old standing, and likewise originated with Bateson, 

 who further compared them both to the craniate pituitary 

 body, "without carrying the comparison into any great detail. 



In the Enteropneusta the excretory function of the regional 

 pores has been superseded by the specialisation of the 

 glomerulus; in Amphioxus by the evolution of the nephric 

 tubules which were discovered by Weiss and Boveri. 



It may indeed be said that in the Enteropneusta the 

 primordia of the nephric tubules are present in the for^ Qf a 

 minute diverticulum at the dorsal medial angle of each gill- 

 pouchy or in a corresponding position in those cases where the 

 gill-pouches are confluent, as in Pt. flava. These structures are 

 particularly well seen in sections through Spengelia alba. 

 Whether this be so or not there is undoubtedly a special 

 significance in the remarkable fact that Boveri's tubules are 

 precisely co-extensive with the gill-clefts, and a renewed 

 importance should be attached to the connecting vessels 

 observed by Paul Mayer between dorsal aorta and sub- 

 intestinal vein in embryos of Pristiurus, which were shown 

 byRiickert to occur in the same segments with the pronephric 

 tubules and to furnish the latter with rudimentary glomeruli. 



' If I understand them aright, MM. Delage and Herouard have completely 

 misunderstood this structure (p. 121, foot-note). 



^ E. W. MacBride, "The Early Development of Amphioxus," 'Quart. 

 Jouru. Micr. Sci.,' vol. 40, 1897, p. 589. 



